The present invention relates to a cooler for use in an exhaust gas recirculation (EGR) system in an internal combustion engine. In particular the invention relates to an exhaust gas cooler which has a bypass line allowing exhaust gases to either pass through the cooler, thereby being cooled, or pass through the bypass line, thereby avoiding cooling.
EGR systems recirculate at least a portion of the engine exhaust gases into the engine air intake system for the purpose of reducing NOx emissions. There is a general requirement to lower vehicular exhaust emissions, including NOx, even further in the light of strict environmental controls. British Patent No 2,303,177 discloses an EGR system in which a portion of the exhaust gases produced by an engine are recirculated from an exhaust line of the engine into an intake line of the engine. In this system a cooler is arranged to cool the recirculated portion of the exhaust gases, and a bypass line is arranged to bypass the cooler. A valve directs the recirculated portion of the exhaust gases to the intake line via the bypass line under low engine temperature and/or load operating conditions, in order to supply hot exhaust gases to the engine under low temperature conditions and during start-up of the engine in order to reduce condensation in the piping and cooler. However British Patent No 2,303,177 does not disclose how the cooler, bypass line and valves are arranged. The cooler and bypass line are provided as separate components, adding to the number of components which must be placed within the limited engine space.
It is an advantage of the present invention to provide a compact EGR system including an EGR cooler and bypass line, which can be fitted readily into an engine compartment.
According to the present invention there is provided an exhaust gas cooler comprising:
an exhaust gas inlet chamber communicating with an exhaust gas inlet,
an exhaust gas outlet chamber communicating with an exhaust gas outlet,
a coolant chamber arranged between said exhaust gas inlet chamber and said exhaust gas outlet chamber and having a coolant inlet and a coolant outlet communicating with the coolant chamber,
a plurality of exhaust gas passages inside the coolant chamber and communicating with the exhaust gas inlet chamber and exhaust gas outlet chamber, and
a means to attach a bypass passage outside the coolant chamber to communicate with the exhaust gas inlet chamber and exhaust gas outlet chamber.
Preferably, the means to attach the bypass passage is integrally formed with the exhaust gas inlet chamber and the exhaust gas outlet chamber.
Preferably, the exhaust gas cooler further comprises a valve assembly arranged at at least one of the exhaust gas inlet chamber and the exhaust gas outlet chamber, the valve assembly being adapted to direct exhaust gas flow through the exhaust gas passages or the means to attach the bypass passage.
Preferably, the valve assembly is arranged at the exhaust gas outlet chamber.
Preferably, the coolant chamber is a tubular chamber and is arranged axially parallel to the bypass passage.
Preferably, the means to attach a bypass passage communicates with the exhaust gas inlet chamber by means of a bypass inlet arranged substantially perpendicular to the direction of flow of exhaust gas through the exhaust gas inlet chamber to the coolant chamber. The means to attach a bypass passage or the bypass passage may comprise an elbow adjacent to the bypass inlet so that the bypass inlet is substantially perpendicular to the axis of the bypass passage when it is attached. Alternatively the exhaust gas inlet chamber may comprise an elbow portion between the coolant chamber and the bypass inlet.
Preferably, the means to attach a bypass passage communicates with the exhaust gas outlet chamber by means of a bypass outlet arranged substantially perpendicular to the direction of flow of exhaust gas through the exhaust gas outlet chamber from the coolant chamber. The exhaust gas outlet chamber may comprise an elbow portion between the coolant chamber and the bypass outlet. Alternatively the means to attach the bypass passage or the bypass passage itself may comprise an elbow adjacent to the bypass outlet so that the bypass outlet is substantially perpendicular to the axis of the bypass passage when it is attached.
Preferably, the valve assembly comprises a valve arranged within the exhaust gas outlet chamber. Preferably, the valve assembly further comprises a motor adapted to drive the valve between an open position in which the valve covers the bypass outlet leaving the exhaust gas outlet chamber open and a closed position in which the valve closes the exhaust gas outlet chamber. The motor may be an electric motor.
Preferably, the bypass passage is formed integrally with the exhaust gas inlet chamber, the exhaust gas outlet chamber and the coolant chamber.
Preferably, the bypass passage includes an expansion means to permit differential thermal expansion of the bypass passage and coolant chamber. Preferably, the bypass passage includes a damping means to assist in vibrational damping of the bypass passage.
The exhaust gas cooler may be provided without a bypass passage and the bypass passage is retro-fitted before use.
Preferably, the exhaust gas passages are exhaust gas tubes. Preferably, the bypass passage is a bypass tube.